BinaryFunctor


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2   // $Id: BinaryFunctor.java,v 1.18 2006/11/30 05:03:42 davidahall Exp $
3   // Copyright (c) 2002-2005  David A. Hall
4   // ============================================================================
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32  
33  package net.sf.jga.fn;
34  
35  import java.io.Serializable  ;
36  import net.sf.jga.fn.adaptor.Bind1st;
37  import net.sf.jga.fn.adaptor.Bind2nd;
38  import net.sf.jga.fn.adaptor.ChainBinary;
39  import net.sf.jga.fn.adaptor.ComposeBinary;
40  import net.sf.jga.fn.adaptor.ComposeUnary;
41  import net.sf.jga.fn.adaptor.Distribute;
42  import net.sf.jga.fn.adaptor.Generate1st;
43  import net.sf.jga.fn.adaptor.Generate2nd;
44  import net.sf.jga.fn.adaptor.Identity;
45  
46  /**
47   * A Function Object that takes two arguments and returns a result.  The two
48   * arguments are of type <code>T1</code> and <code>T2</code>, and
49   * the result is of type <code>R</code>
50   * <p>
51   * Copyright &copy; 2002-2005  David A. Hall
52   *
53   * @author <a HREF="mailto:davidahall@users.sourceforge.net">David A. Hall</a>
54   **/
55  
56  abstract public class BinaryFunctor<T1,T2,R> extends Functor<R> implements Serializable  ,Visitable {
57      /**
58       * Executes the function and returns the result.
59       */
60      abstract public R fn(T1 arg1, T2 arg2);
61  
62      /**
63       * Factory method that creates a UnaryFunctor that binds a constant value to
64       * this' first argument.  Given argument <b>x</b>, the new functor will
65       * return <code>fn<sub>this</sub>(value, x)</code>
66       */
67      public UnaryFunctor<T2,R> bind1st (T1 value){
68          return new Bind1st<T1,T2,R>(value, this);
69      }
70  
71      /**
72       * Factory method that creates a UnaryFunctor that binds a constant value to
73       * this' second argument.  Given argument <b>x</b>, the new functor will
74       * return <code>fn<sub>this</sub>(x, value)</code>
75       */
76      public UnaryFunctor<T1,R> bind2nd (T2 value){
77          return new Bind2nd<T1,T2,R>(value, this);
78      }
79  
80      /**
81       * Factory method that creates a Generator that binds constant values to
82       * this' arguments.  The new generator will return
83       * <code>fn<sub>this</sub>(value1, value2)</code>
84       */
85      public Generator<R> bind (T1 value1, T2 value2) {
86          return bind1st(value1).bind(value2);
87      }
88  
89      /**
90       * FactoryMethod that creates a UnaryFunctor that passes its argument to
91       * each of the given functors, and uses the results as the arguments to this
92       * function. Given argument <b>x</b>, the new functor will return
93       * <code>fn<sub>this</sub>(g(x), h(x))</code>
94       */
95      public <F> UnaryFunctor<F,R> compose (UnaryFunctor<F,T1> g, UnaryFunctor<F,T2> h) {
96          return new ComposeUnary<F,T1,T2,R>(g,h,this);
97      }
98  
99      /**
100      * FactoryMethod that creates a BinaryFunctor that passes its argument to
101      * each of the given functors, and uses the results as the arguments to this
102      * function. Given arguments <b>x</b> and <b>y</b>, the new functor will
103      * return <code>fn<sub>this</sub>(g(x,y), h(x,y))</code>
104      */
105     public <F1,F2> BinaryFunctor<F1,F2,R>
106     compose (BinaryFunctor<F1,F2,T1> g, BinaryFunctor<F1,F2,T2> h)
107     {
108         return new ComposeBinary<F1,F2,T1,T2,R>(g,h,this);
109     }
110 
111     /**
112      * FactoryMethod that creates a BinaryFunctor that passes each of its two
113      * arguments to a pair of UnaryFunctors, then uses the results as arguments
114      * to this function.  Given arguments <b>x</b> and <b>y</b>, the new functor
115      * will return <code>fn<sub>this</sub>(g(x), h(y))</code>.  Note: this
116      * method cannot be called compose, as it is only distinct from the unary
117      * form of compose in its param types and its return type
118      */
119     public <F1,F2> BinaryFunctor<F1,F2,R> distribute (UnaryFunctor<F1,T1> g, UnaryFunctor<F2,T2> h)
120     {
121         return new Distribute<F1,F2,T1,T2,R>(g,h,this);
122     }
123 
124     /**
125      * FactoryMethod that converts this functor to a UnaryFunctor by using the
126      * given generator to produce the first argument.  Given argument <b>y</b>,
127      * the new functor will return <code>fn<sub>this</sub>(gen(), y)</code>.
128      */
129     
130     public UnaryFunctor<T2,R> generate1st(Generator<T1> gen) {
131         return new Generate1st<T1,T2,R>(this, gen);
132     } 
133 
134     /**
135      * FactoryMethod that converts this functor to a UnaryFunctor by using the
136      * given generator to produce the first argument.  Given argument <b>x</b>,
137      * the new functor will return <code>fn<sub>this</sub>(x, gen())</code>.
138      */
139     
140     public UnaryFunctor<T1,R> generate2nd(Generator<T2> gen) {
141         return new Generate2nd<T1,T2,R>(this, gen);
142     } 
143 
144     /**
145      * FactoryMethod that converts this functor to a Generator by using the two
146      * given generators to produce the arguments.  The new functor will return
147      * <code>fn<sub>this</sub>(gen1(), gen2())</code>.
148      */ 
149     
150     public Generator<R> generate(Generator<T1> gen1, Generator<T2> gen2) {
151         return generate1st(gen1).generate(gen2);
152     } 
153 
154     // -----------------
155     // Functor interface
156     // -----------------
157     
158     public R eval(Object  ... args) {
159         // @SuppressWarnings
160         // This generates two unchecked cast warnings: we're crossing the line from
161         // unsafe rawform code to typesafe generic code.  This interface is known
162         // to be unsafe, and documented to the user as such.        
163         return fn((T1) args[0], (T2)args[1]);
164     }
165 
166     // -------------------
167     // Visitable interface
168     // -------------------
169     
170     /**
171      * No-op implementation of Visitable interface.
172      */
173     public void accept(Visitor v) {}
174 } 
175
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